So, first you need to define a ClassID in the .inccar files... for this e.g I'll use ClassID=DTM08
now you need to create 3 .tga menu icons named:
MenuButton_ClassSelect_DTM08_Disabled.tga
MenuButton_ClassSelect_DTM08_MouseOver.tga
MenuButton_ClassSelect_DTM08_Normal.tga
You will use your ClassID where DTM08 is in the above e.g.
these all need to be 256x128 px with alpha layer.
Start by making the MouseOver first, then copy it and reduce the colour and remove some alpha to grey it out a little and save that as Normal, then starting with MouseOver again, convert it to grey scale colours and have a play with alphas again, then save all three to:
...\race 07\UIData\Menu\Textures_Frog
...\race 07\UIData\Menu\Textures_Mamba
...\race 07\UIData\Menu\Textures
This will make sure that the icons work when the game is run via Race07, GTR Evo or STCC interface...